The present invention relates to non-coherent optical convolvers that process optical images in general convolution functions.
A difference-of-Gaussian's technique is an optical image process which convolves an original image with two separate Gaussian functions and subtracts the results. Present implementation of the difference-of-Gaussian algorithm are carried out on digital computers, and require both extensive hardware and relatively long computational times.
The task of processing optical images in general convolution functions and, more specifically, in a Gaussian convolution, using a direct application of optical elements on an original image, is alleviated to some extent by the following U.S. Patents, which are incorporated herein by reference:
U.S. Pat. No. 3,510,223 issued to A. W. Lohman on May 5, 1970; PA0 U.S. Pat. No. 3,544,197 issued to C. S. Weaver on Dec. 1, 1970; PA0 U.S. Pat. No. 3,809,873 issued to C. N. Klahr on May 7, 1974; PA0 U.S. Pat. No. 4,023,037 issued to H. Weiss on May 10, 1977; PA0 U.S. Pat. No. 4,173,720 issued to R. J. Geluk on Nov. 6, 1979; and PA0 U.S. Pat. No. 4,282,510 issued to P. D. Southgate on Aug. 4, 1981.
The Lohman reference discloses an optical cross-correlation and convolution method wherein a coherent light beam is directed towards a converging lens, with a pair of diffraction gratings that revolve around each other, producing a changing grating interval.
The Weaver patent discloses an optical signal processing method for convolving functions. (A collimated laser beam shines through a pair of transparencies containing the functions to be convoluted).
The klahr patent discloses an optical processor for convolution filtering or optically processing two-dimensional convolution integrals. The apparatus is particularly concerned with processing electrical signals from two-dimensional data arrays such as used in synthetic aperture radar.
The Southgate patent discloses a system for the analysis of an optical sensed field and provides for convolving of spatial two-dimensional fields of intensity. Convolving is performed by a signal processor including detector elements and optical and electronic processors. The apparatus employs a diffused light source, an imaging lens and a Gaussian filter.
The Weiss et al patent discloses a method of decoding three-dimensional images using incoherent light or x-rays. Decoding of the image is effected by shifting between an illumination lens and a point hologram in an incoherent monochromatic converging beam.
The Geluk patent discloses an apparatus for image construction wherein a cross-sectional image is constructed from a plurality of profiles by means of back projection. The apparatus uses analog convolution with two-dimensional or one-dimensional function.
The use of digital computers to produce a Gaussian convolution of an image is an unnecessary complexity. The simplest and most direct approach is to process the image with a suitably designed optical element to optically convolve the original image with the desired Gaussian distribution. Additionally, for the desired application of the Gaussian distribution, there exists the need to smoothly vary the size of the Gaussian function. The present invention is intended to satisfy that need.